GSTM1 and sickle cell disease: GBT440, an analog of GBT1118 that increases Hb–O2 affinity and arterial O2 loading as well, is currently in clinical trials for the treatment of sickle cell disease and has demonstrated excellent safety and biological effects in both healthy subjects and subjects with sickle cell disease (NCT02285088, http://clinicaltrials.gov/) (Oksenberg et al.